Unveiling catalytic potential and the native role of PETase from Streptomyces sp

Polyethylene terephthalate (PET) is one of the most widely produced thermoplastics, valued for its durability and low cost, yet it contributes significantly to global environmental pollution. The discovery of PET-degrading enzymes in Actinobacteria inspired a bioinformatics search for novel PET hydrolases in Streptomyces species from Chile's Atacama Desert. We selected PETS26b for detailed characterization. Genomic context revealed conserved CAZymes adjacent to PETS26b. Biochemical characterization showed optimal activity at 28°C and pH 8.0. PETS26b exhibited broad substrate specificity toward p-nitrophenyl esters, with superior catalytic efficiency toward p-nitrophenyl octanoate (kcat/Km = 2.92 × 10⁶ M^-1 s^-1) relative to other reported esterases. The enzyme also hydrolyzed PET powder and bis(2-hydroxyethyl) terephthalate (BHET), and deacetylated glucose pentaacetate, consistent with generalist esterase activity. Overall, docking analyses revealed favorable docking scores for 4-nitrophenyl esters and PET-related substrates within the active site, with predicted docking scores showing good agreement with experimental kinetic data. Moreover, PETS26B accommodated variably acetylated carbohydrate oligosaccharides, displaying particularly favorable binding scores for highly acetylated substrates. These findings highlighted the versatile roles of PET-degrading enzymes in the degradation of plant biomass esters.